The aim of this work is to understand the organization and evolution of the SUC gene family of yeast. The SUC genes (SUC1-SUC5) are a dispersed family of genes encoding the sucrose-Hydrolyzing enzyme invertase. Closely related yeast strains often carry SUC+ genes at different chromosomal loci. Physical analysis has shown that the SUC+ genes are homologous and that a strain lacking a SUC+ allele at a given locus usually has no SUC DNA sequence at that locus. Thus, it appears that SUC genes have transposed during the evolution of closely related strains. The goals of this proposal are to analyze the homology between different SUC+ loci (i.e., the SUC+ gene and flanking sequences) and to compare SUC loci carrying SUC+ alleles with the corresponding loci lacking SUC DNA sequences. These studies will define the structure of the SUC gene family and should suggest likely mechanisms for its evolution.